In the battery, the power generating element is formed by winding the long foil-shaped positive electrode plate and the long foil-shaped negative electrode plate, with the separators sandwiched therebetween, about the winding core to thereby increase areas of the positive and negative plates facing each other to maximize energy density of the battery.
As the power generating element formed by winding the foil-shaped positive electrode plate and the like about the winding core in this manner, in many cases, the foil-shaped positive electrode plate and the like are wound about the circular cylindrical winding core, the power generating element in a circular columnar shape as a whole, in its unchanged shape, is housed into a battery case, and the battery case is also formed in a circular columnar shape adapted to the shape of the power generating element.
On the other hand, as described in the following Patent Document 1, forming a power generating element into a flat shape and also forming a battery case for housing the power generating element into a thin shape are widely practiced.
By the formation of the battery case into the thin shape in this manner, it is possible to efficiently dispose the battery in a small space.
As a manufacturing process of this type of power generating element in the flat shape, the foil-shaped positive electrode plate and the like are wound about the cylindrical winding core and then the wound object is flattened into the flat shape in many cases.